The most common and most likely answer to this crossword clue is the 10 letter word AMBASSADOR
I've seen this crossword clue in The Times
A
M
B
A
S
S
A
D
O
R
More clues leading to the result AMBASSADOR
- Seen in Durham, bass adores diplomat
- In alternative case he could be one
- He’ll represent people if he’s given a different case
- A commercial, alternatively, featuring male singer in rep
- Sam’s abroad, working as a diplomat
- Welsh politician low on gas receives note from diplomat
- Diplomat dancing samba, pathetic otherwise
- In capitals, he could be a diplomat
- Graduates down in foreign capital upset official
- Diplomat, a male, so sad, drunk in pub
Buddy explains!

The straight part
We know that "rep" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case rep = ambassador.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does AMBASSADOR mean?
AMBASSADOR noun- A minister of the highest rank sent to a foreign court to represent there his sovereign or country. (Sometimes called ambassador-in-residence)
- An official messenger and representative.
- A corporate representative, often the public face of the company.